1. Field of the Invention
This invention relates generally to low fluid level detectors and more particularly to the detection of low fluid levels in humidifiers as used in medical respiratory apparatus.
2. Description of the Prior Art
Humidifiers used in inhalation therapy incorporate a fluid reservoir in which the fluid capacity is kept small in order to minimize changes in pneumatic system compliance resulting from depletion of the fluid. It thus becomes necessary to refill the reservoir periodically. Prior art visual fluid level markings on the reservoir did not command the necessary attention. At least some float switches, conductivity sensors, etc., employed to detect low fluid level in the prior art have suffered from lack of upkeep by the user, thus when most needed, were inoperative.
A novelty search conducted in the United States Patent and Trademark Office to locate patents relevant to the above topic did not disclose any patents contemplating the instant means of fluid level detection. The following, however, were considered to be of potential interest:
______________________________________ Patent No. Title Inventor ______________________________________ 3,461,907 "Liquid Level Control Device for C. P. Wood, Jr. Refrigeration Systems" 2,619,566 "Actuating Apparatus Responsive C. F. Mahoney to Change in Fluid Level" 3,703,693 "Liquid Level Sensing System" R. N. Levinn 3,335,243 "Bimetal Indicator Device with a J. R. Canaday Heater Energized Under all Oper- ative Conditions" 3,029,354 "Level Control and Indicating J. E. Watkins Mechanism" 2,570,451 "Liquid Level Control System" F. W. Hottenroth 2,675,019 "Liquid Level Control" P. F. Shivers ______________________________________
The fields of search were:
Class 137 Subclass 386
It would thus be a great advantage to the art to provide a low fluid level detection means.
Another advantage would be the provision of a low fluid level detection means having no moving parts, thus requiring no user maintenance.
A further desirable advantage would be the provision of such a detection means independent of periodic calibration.